Referring to FIG. 1, as known in the art of electronic prepress systems, output devices, such as imagesetters and platesetters, and, more recently, direct on-press imaging systems, have been served by a dedicated raster image processor (“RIP”) connected between a front end computer (“front end”) and an output device. In the prepress system of the prior art, page images 90 are designed and imposed on the front end 40.
Imposition application software electronically positions individual pages coded in a page description language onto an electronic representation of a press sheet to form a flat 95, i.e. a multi-page press sheet image. To accomplish this layout, the software combines the page description language data of individual pages and graphics files into a single page description language file and then adds cutting, folding, and other custom flat marks, thereby creating a fully-imposed flat 95. The flat 95 is transmitted to the RIP 34 for processing as a single file.
Various front-end software application programs produce output in a page description language. Page description languages, such as Postscript™ and PDF™, offered by Adobe Systems of Mountain View, Calif., allow text descriptions of large image data files to be transferred efficiently over communication lines and data networks, because page description language code is generally significantly smaller in data size than the raster data that results from the interpreted page description language code. When a page description language image file data is received by the RIP, operations such as font processing, image placement, trapping, and color separating result in a final output file, which is configured for a proofer 68, which is used to view images on paper in a simulation of the final, printed product, or another output device 46.
The raster data produced by the RIP for an imagesetter or platesetter is binary, meaning that each pixel in the image is either on or off. Color images are represented in separations. Each separation is imaged separately to the imagesetter or platesetter. The separations imaged by the output device are used to make printing plates (in the case of imagesetters) or are the printing plates themselves (in the case of platesetters).
Images generated for output by a RIP to a proofer are typically contone images (meaning that each pixel has some color value) rather than binary separations, and so the RIP output for a proofer will typically be different than the RIP output generated for an imagesetter or platesetter. Because the images are different, there is a danger of artifacts being present in the proofed image that are not present in the separations generated for a raster imaging system or vice-versa. It would be useful, therefore, to provide proof images that accurately reflect imaged separations.
If the rasterized flat 97 is submitted to the proofer 68, the proofer output is inspected. If no errors in the imposition scheme or color reproduction have been detected in the proofer output, the rasterized flat 97 is ready for output, and is transmitted again to the RIP 34 for processing for the output device 46. If a correction or other last-minute design or imposition change is necessary, the entire flat 95 is re-submitted to the RIP 34 for re-processing after the error has been corrected or the change has been made on the front end 40. The rasterized flat 97 may first be RIP-processed for the proofer 68, and the process is repeated if another error is detected.
Recent use of large-format imagesetters and platesetters goes well beyond creation of single pages. These output devices produce press size “flats” or “press sheets” in film or plate that contain four, eight, or more pages. After printing on a press, the press sheet is then cut and folded to become part of a paper document, such as a book or a magazine. Prepress imposition design of a press sheet is traditionally performed at the front end using imposition application software. This software electronically positions individual pages coded in a page description language, such as PostScript or PDF, onto an electronic representation of a press sheet. To accomplish this layout, the imposition software combines the PostScript or PDF data of individual pages into a single PostScript or PDF file and adds cutting, folding, and other custom marks, thereby creating a multi-page press sheet image. This image is then submitted for processing by the RIP to prepare a bitmap image file for transfer to the output device. It is, thus, necessary to have all individual pages of the print job available prior to RIP-processing. Moreover, a new imposition layout must be set for every new print job, even when processing a print job with the same number of pages of the same size as the job previously processed.
The page description language code that must be interpreted to image multiple pages in one press sheet is very complex, and the resulting bitmaps are very large. As a result, the RIP may be a bottleneck in creating press sheet films and plates. RIP-processing time for complex images can require several multiples of the imaging time. RIP-processing time has a greater impact on workflow when a change is required in a complex image. This is because a change in even a part of one page on a multi-page press sheet generally requires that the RIP reprocess the entire press sheet image. The bottleneck of slow RIP speeds affects the workflow both the first time the press sheet was processed by the RIP and a second (or more) time(s) when a modified version of the press sheet image is processed.
This method is inefficient and time-consuming, because a change in even a part of one page of the flat generally requires that the RIP reprocess the entire flat. In addition, the processing of a single raster image is further complicated by the necessity of processing all of the page image data at the same time. The page description language code that must be interpreted to image multiple pages onto a single press sheet is very complex, and the resulting bitmaps are very large. As a result, RIP-processing time for complex images can be much slower than the processing of individual pages separately. The bottleneck of slow RIP speeds affects the workflow both the first time the flat 95 is processed by the RIP and then each time when a modified version of the flat is processed.
One alternative to reprocessing the entire image, when a modification to a RIP processed image is desired, has been to physically modify the film that is output by an imagesetter to make a plate. To accomplish this modification, a portion of the image to be modified is physically cut from the film, and if necessary, a correction film inserted in its place. This can be difficult to accomplish without adding imaging artifacts. More importantly, this alternative is not available with direct-to-plate technology that does not use film. This alternative is also not possible when the change required is to lay out the various pages in a flat differently so as to accommodate a different press than the one that was originally intended.
It should be noted that one goal of modern electronic prepress systems is to keep the printing press, which is a very expensive resource, as busy as possible. It would be useful, therefore, to provide a prepress imaging system that could quickly accommodate addition of pages to a pending print job, or changes to content of individual pages, imposition layout of large-format multi-page press sheets, or press configuration, without having to wait for the modified press sheet to be re-processed by the RIP. If, for example, a first press breaks or is busy, and another (second) press is available, it would be useful to quickly provide flats that are configured for the second press.
In addition, when a multi-page flat has been imaged on a proofer, it is typical to measure the size and location of the pages in the flat to verify that the pages are aligned properly for the particular printing press on which printing is intended. It may not be easy, however, to determine whether the page has been positioned on the press sheet such that the bleed areas extend sufficiently over the cut marks. The measurements differ for each flat based on the pages in the flat and the layout and press for which the flat is intended. Because this is a manual measurement process, it is time-consuming and prone to error. It would, therefore, be useful to allow for faster measurement and verification of the layout when viewing a proof image.